The necessity of environmentally friendly replacements for commodity plastics has stimulated the development of polymers from bio-renewable sources. A notable example is polylactide, a commercially important material derived from lactic acid. Recent efforts in the chemical industry have been focused on new bio-derived starting materials that can be used for the preparation of new plastics, as well as other useful products and precursors. One example of an important bio-derived starting material is 3-hydroxypropionic acid (3-HP), a structural isomer of lactic acid, which comprises the repeat unit of a useful polymer, poly(3-hydroxypropionic acid) (P[3-HP]). High molecular weight P[3-HP] has attractive mechanical properties, such as rigidity, ductility, and exceptional tensile strength in drawn films. In addition, P[3-HP] is enzymatically and hydrolytically degradable, thus enhancing its environmental appeal.
P[3-HP] has been prepared by the condensation of 3-HP esters and the ring-opening polymerization (ROP) of β-propiolactone, but both methods suffer from disadvantages. Relative to condensations, ROP generally provides a greater degree of control over molecular weight, co-monomer incorporation, and end group definition. Yet while highly strained β-propiolactone can readily be ring opened to yield high molecular weight P[3-HP], it is carcinogenic and its large-scale synthesis is difficult, especially when starting with the preferred precursor 3-HP. Thus, it would be desirable to develop an alternative ROP route to P[3-HP] that avoids the use of β-propiolactone. Additionally, it would be desirable to develop new methodology for the preparation of high molecular weight P[3-HP] that is derived directly from bio-renewable sources such as 3-HP.